I have an '11 335xi with the iPod/USB option and use a 5th Gen 30gb iPod with the original iPod cable. The first few days everything was fine but recently when I get in the car the iPod says "Very low battery, please wait" and my commute is only 10 minutes so I'm guessing it doesn't have a chance to do charge up.
The first day it did this, I took it out, had to reset it a bunch of times and got it up and running and plugged into my computer. Let it charge overnight, put it in the car and it was running perfectly. Came back at the end of the day and it's dead again. Sometimes, randomly though, the iPod will start working again when I drive to the gym, park for an hour and come back. This just leads me to believe that the iPod/USB port is not turning off the iPod when the car turns off, leading it to drain. Is this normal?

What do you guys think my next course of action should be? Try a different cable, different iPod, take in it to service?

The iPod is 4 years old so I would be inclined to think that was the source of the problem, but the fact that it was working with the iPod adapter in my C300 previously and worked the first few days in the 335 makes me think otherwise.

What do you guys think my next course of action should be? Try a different cable, different iPod, take in it to service?

Does the battery charge at all while you're driving? Does it go up a %age, or down? The 6FL doesn't provide a lot of current, and maybe your iPod needs more than it can handle. The iPhone 3GS and 4 don't charge with the base cable, either.

Based on how old it is, it's not a touch ipod is it? I am having a problem w mine as well and only noticed the battery sucks because I recently flew and took my ipod touch out of my armrest. In my case, it was a matter of not closing out programs and apps and also, iOS4 apparently has a bug that drains battery. Thanks Apple, I didn't pay $400 for a second ipod touch only to have the battery work for one hour. Check the OS you're running. Your car does automatically charge and shut off the ipod when not in use.